Wierd (obviously a bug).
I assume (the perversity of the universe tending to the ultimate) that it dropped in one of the rooms that you can only get into after you demonstrate your ability to create rifts and see the elder.
Don't forget that the NW room with no door can be reached by teleporter from a SE room - the teleporter being partly hidden by some furniture. What I don't recall off hand is whether that SE room is one of the ones that you can only get into after seeing the elder - I mention this just in case it isn't.
Presumably if you reload and kill Sammy again the drop will be in a different spot.
